U.S. patent number 6,037,709 [Application Number 09/075,827] was granted by the patent office on 2000-03-14 for cathode ray tube.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Shinichiro Nakagawa, Norio Shimizu.
United States Patent |
6,037,709 |
Nakagawa , et al. |
March 14, 2000 |
Cathode ray tube
Abstract
A cathode ray tube includes a panel having a substantially
rectangular effective surface and a substantially rectangular skirt
portion standing on the periphery of the effective surface, a
shadow mask having a substantially rectangular mask body and a mask
frame supporting the mask body and opposed to the skirt portion,
and a holder provided between the skirt portion of the panel and
the mask frame of the shadow mask and elastically suspending the
mask frame to the panel. The holder comprises a first member having
an engagement portion engaged with a stud pin attached on the skirt
portion, and a second member having a fixing portion fixed to the
mask frame. The plate-thickness of the first member is smaller than
that of the second member, and the length of a first slanting
portion of the first member is smaller than the length of a second
slanting portion of the second member. With use of this holder, a
color drift caused by an external impact undesirably applied to the
cathode ray tube and a color drift caused by a thermal expansion of
the mask frame during operation for a long time can simultaneously
be corrected and an image of excellent quality can be displayed
stably.
Inventors: |
Nakagawa; Shinichiro (Fukaya,
JP), Shimizu; Norio (Fukaya, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Kawasaki, JP)
|
Family
ID: |
14798408 |
Appl.
No.: |
09/075,827 |
Filed: |
May 12, 1998 |
Foreign Application Priority Data
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|
|
|
May 12, 1997 [JP] |
|
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9-120926 |
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Current U.S.
Class: |
313/404;
313/407 |
Current CPC
Class: |
H01J
29/073 (20130101) |
Current International
Class: |
H01J
29/07 (20060101); H01J 029/07 () |
Field of
Search: |
;313/402,404,405,406,407 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Patel; Ashok
Attorney, Agent or Firm: Pillsbury Madison & Sutro
LLP
Claims
We claim:
1. A cathode ray tube comprising:
a face panel having a substantially rectangular effective portion,
a side wall portion standing along a peripheral edge portion of the
effective portion, and a plurality of stud pins projected from an
inner surface of the side wall portion;
a phosphor screen formed on an inner surface of the effective
portion of the face panel;
a shadow mask having a substantially rectangular mask body and a
substantially rectangular mask frame, the mask body being provided
inside the face panel and having a plurality of apertures opposed
to the phosphor screen, and the mask frame supporting a peripheral
edge portion of the mask body and opposed to the side wall portion
of the face panel;
a plurality of support members fixed to the mask frame and
respectively engaged with the stud pins of the face panel, thereby
elastically supporting the mask frame on the face panel;
an electron gun for emitting an electron beam onto the phosphor
screen through the plurality of apertures of the mask body; and
a deflector for deflecting the electron beam emitted from the
electron gun,
wherein
each of the support members has first and second members each
formed by bending a narrow long plate-like member having an
elasticity,
the first member has an engagement portion engaged with the stud
pin, a first connection portion connected with the second member,
and a first slanting portion slanted and extended from the first
connection portion toward the engagement portion, in a direction in
which the first member is apart from the second member,
the second member has a fixing portion fixed to the mask frame, a
second connection portion connected with the first connection
portion of the first member, and a second slanting portion slanted
and extended from the second connection portion toward the fixing
portion, in a direction in which the second member is apart from
the first member, and
the first member has a plate-thickness d1 smaller than a
plate-thickness d2 of the second member, and the first slanting
portion has a length L1 smaller than a length L2 of the second
slanting portion.
2. A cathode ray tube according to claim 1, wherein an angle
.theta.1 between the first slanting portion of the first member and
the engagement portion is larger than an angle .theta.2 between the
second slanting portion of the second member and the fixing
portion.
3. A cathode ray tube according to claim 1, wherein an angle .phi.1
of the first slanting portion to a tube axis of the cathode ray
tube is larger than an angle .phi.2 of the second slanting portion
to the tube axis.
4. A cathode ray tube according to claim 3, wherein the length L1
and the angle .phi.1 of the first slanting portion and the length
L2 and the angle .phi.2 of the second slanting portion satisfy a
relation of L1.times.cos.phi.1<L2.times.cos.phi.2.
5. A cathode ray tube according to claim 1, wherein the first
connection portion of the first member is extended in a direction
in which the first slanting portion is extended.
6. A cathode ray tube comprising:
a face panel having a substantially rectangular effective portion,
a side wall portion standing along a peripheral edge portion of the
effective portion, and four stud pins provided to be projected from
inner surfaces of four corner portions of the side wall
portion;
a phosphor screen formed on an inner surface of the effective
portion of the face panel;
a shadow mask having a substantially rectangular mask body and a
substantially rectangular mask frame, the mask body being provided
inside the face panel and having a plurality of apertures opposed
to the phosphor screen, and the mask frame supporting a peripheral
edge portion of the mask body, being opposed to the side wall
portion of the face panel, and having a higher thermal expansion
coefficient than the mask body;
four support members respectively fixed to four corner portions of
the mask frame and respectively engaged with the four stud pins of
the face panel, thereby elastically supporting the mask frame on
the face panel;
an electron gun for emitting an electron beam onto the phosphor
screen through the plurality of apertures of the mask body; and
a deflector for deflecting the electron beam emitted from the
electron gun,
wherein
each of the four support members has first and second members each
formed by bending a narrow long plate-like member having an
elasticity,
the first member has an engagement portion engaged with the stud
pin, a first connection portion connected with the second member,
and a first slanting portion slanted and extended from the first
connection portion toward the engagement portion, in a direction in
which the first member is apart from the second member,
the second member has a fixing portion fixed to the mask frame, a
second connection portion connected with the first connection
portion of the first member, and a second slanting portion slanted
and extended from the second connection portion toward the fixing
portion, in a direction in which the second member is apart from
the first member,
the first member has a plate-thickness d1 smaller than a
plate-thickness d2 of the second member, and the first slanting
portion has a length L1 smaller than a length L2 of the second
slanting portion,
an angle .theta.1 between the first slanting portion of the first
member and the engagement portion is larger than an angle .theta.2
between the second slanting portion of the second member and the
fixing portion, and
an angle .phi.1 of the first slanting portion to a tube axis of the
cathode ray tube is larger than an angle .phi.2 of the second
slanting portion to the tube axis.
7. A cathode ray tube according to claim 6, wherein the length L1
and the angle .phi.1 of the first slanting portion and the length
L2 and the angle .phi.2 of the second slanting portion satisfy a
relation of L1.times.cos.phi.1<L2.times.cos.phi.2.
8. A cathode ray tube according to claim 6, wherein the first
connection portion of the first member is extended in a direction
in which the first slanting portion is extended.
Description
BACKGROUND OF THE INVENTION
The present invention relates to a cathode ray tube comprising a
plurality of support members for suspending a mask frame on a face
panel.
In general, a cathode ray tube comprises a panel having a
substantially rectangular skirt portion standing on the periphery
of a substantially rectangular effective surface, a funnel
connected with the skirt portion of the panel, a phosphor screen
formed inside an effective surface of the panel, a shadow mask
having a substantially rectangular mask body where a number of
electron beam apertures are formed and a substantially rectangular
mask frame attached on the periphery of the mask body, a plurality
of support member for elastically suspending the shadow mask on the
panel such that the mask body is opposed to the phosphor screen, an
electron gun provided in a neck portion of the funnel to emit an
electron beam to the phosphor screen through electron beam
apertures of the mask body, and a deflector for generating a
magnetic field to deflect the electron beam emitted from the
electron gun.
Thus, the electron beam emitted from the electron gun is deflected
by the deflector and the phosphor screen is scanned in the
horizontal and vertical directions through the shadow mask, thereby
displaying a color image through the panel.
A holder 40 having a substantial wedge-like shape as shown in FIG.
11 is known as a support member for supporting the shadow mask. The
holder 40 has a side fixed on the mask frame 42 of the shadow mask
and another side detachably engaged on a stud pin provided so as to
project from the skirt portion 44.
To display an image without a color drift on the phosphor screen
46, the electron beam passing through an electron beam aperture in
the shadow mask must be landed correctly on a predetermined
position on the phosphor screen 46. Therefore, the positional
relationship between the panel and the shadow mask, and
particularly, the distance between the inner surface of the panel
where the phosphor screen 46 is formed and the mask body where a
number of electron beam apertures 45 are formed must be maintained
with high precision.
However, if the mask body is made of a thin carbon steel plate or
the like, the mask body is thermally expanded by the collision of
the electron beam during operation for a long time, toward the
phosphor screen 46, i.e., so-called doming is caused. When the mask
body thus causes doming, the distance therefrom to the inner
surface of the panel is changed and the landing of the electron
beam is misregistered, thereby causing a color drift in the display
image.
Therefore, the color drift caused by the doming of the mask body is
compensated by using the substantially wedge-like holder 40 as
described above. This means that the holder 40 is deformed as
indicated by a one-dot chain line in the figure when doming occurs
in the mask body and the mask body is pushed up in the direction
toward the phosphor screen 46. In this manner, the landing position
of the electron beam is compensated so that the position is not
changed before and after the thermal expansion of the shadow
mask.
In addition, as for a cathode ray tube of a relatively large size,
it is known to form the mask body from an invar material having a
lower thermal expansion coefficient than the mask frame. Thus, in a
cathode ray tube having a mask body having a lower thermal
expansion coefficient than the mask frame, the holder 50 as shown
in FIG. 12 is used.
The holder 50 has a first member fixed to the mask frame 52 of the
shadow mask, and a second member engaged on the stud pin 53
projected from the skirt portion 54 of the panel. The holder 50 is
formed to have a substantially V-shaped cross-section which is
symmetrical in the lateral direction.
If this kind of cathode ray tube is operated for a long time, the
mask body is little thermally expanded but only the mask frame 52
is thermally expanded as indicated by a one-dot chain line in the
figure. In this time, the shadow mask is not moved in a direction
in which the shadow mask is apart from and close to the phosphor
screen 56 since the holder 50 is formed to be symmetrical in the
lateral direction. This means that the landing position of the
electron beam can be maintained at a correct position even if the
mask frame is thermally expanded.
However, even if the counter measure as described above is taken,
in most cases of recent cathode ray tubes having a relatively large
deflection angle, a color drift caused by misregistration of the
landing position of the electron beam. To compensate such electron
beam landing misregistration, the mask frame 52 needs to be moved
in a direction in which the frame 52 is apart from the phosphor
screen 56, i.e., toward the electron gun. Specifically, to cancel
heat expansion of the mask body toward the phosphor screen 56,
deformation of the holder due to thermal expansion of the mask
frame must cause the mask frame to move toward the electron
gun.
For example, Japanese Patent Application KOKAI Publication No.
1-14851 discloses an example of a technique of moving the mask
frame toward the electron gun. Disclosed in this publication is a
holder having a first member which is engaged on a skirt portion of
a panel and has a greater plate-thickness than a second member
fixed on the mask frame. If the plate-thickness of the first member
is thus thickened, the first member tends to be deformed less
easily than the second member. As a result, when the mask frame is
thermally expanded, the second member is more deformed than the
first member, so that the mask frame is moved toward the electron
gun.
However, in this holder, a stress is concentrated on the second
member having a smaller thickness than the first member when an
undesired impact is applied from the outside of the cathode ray
tube. Consequently, the second member which is relatively weak and
tends to be easily deformed is plastically deformed and
misregistered landing is caused due to the deformation of the
second member, if the impact from the outside cannot be
absorbed.
As a technique for preventing misregistered landing due to an
external impact, Japanese Patent Application KOKOKU Publication No.
64-27144 proposes a holder 40 having bending portions 40a and 40b.
The bending portions 40a and 40b function to restrict a movement of
the mask frame against an external impact from a direction vertical
to the page surface in FIG. 11, but is not effective against an
external impact from the direction of the tube axis of the cathode
ray tube.
Also discussed is a method of improving the rigidity of respective
components of the holder to hinder plastic deformation. However, if
this method is adopted, it is not possible to correct sufficiently
a color drift caused under influences from a heat when the cathode
ray tube is operated for a long time, but also the detachability of
the holder during manufacturing steps is degraded.
As described above, the shape of the holder holding the shadow mask
is important to display an image on a phosphor screen of a cathode
ray tube without a color drift. However, it is difficult for
conventional techniques to provide a holder which is capable of
simultaneously correcting both a color drift caused by a change of
the positional relationship between the shadow mask and the panel
due to an external impact and a color drift caused due to
influences from a heat when the cathode ray tube is operated for a
long time.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in view of the respects
described above and has an object of providing a color cathode ray
tube capable of simultaneously correcting a color drift caused by
an external impact and a color drift caused by a thermal expansion
so that an image of high quality can be stably displayed.
To achieve the above object, the cathode ray tube according to
claim 1 of the present invention cathode ray tube comprises: a face
panel having a substantially rectangular effective portion, a side
wall portion standing along a peripheral edge portion of the
effective portion, and a plurality of stud pins projected from an
inner surface of the side wall portion; a phosphor screen formed on
an inner surface of the effective portion of the face panel; a
shadow mask having a substantially rectangular mask body and a
substantially rectangular mask frame, the mask body being provided
inside the face panel and having a plurality of apertures opposed
to the phosphor screen, and the mask frame supporting a peripheral
edge portion of the mask body and opposed to the side wall portion
of the face panel; a plurality of support members fixed to the mask
frame and respectively engaged with the stud pins of the face
panel, thereby elastically supporting the mask frame on the face
panel; an electron gun for emitting an electron beam onto the
phosphor screen through the plurality of apertures of the mask
body; and a deflector for deflecting the electron beam emitted from
the electron gun, and is wherein each of the support members has
first and second members each formed by bending a narrow long
plate-like member having an elasticity, that the first member has
an engagement portion engaged with the stud pin, a first connection
portion connected with the second member, and a first slanting
portion slanted and extended from the first connection portion
toward the engagement portion, in a direction in which the first
member is apart from the second member, that the second member has
a fixing portion fixed to the mask frame, a second connection
portion connected with the first connection portion of the first
member, and a second slanting portion slanted and extended from the
second connection portion toward the fixing portion, in a direction
in which the second member is apart from the first member, and that
the first member has a plate-thickness d1 smaller than a
plate-thickness d2 of the second member, and the first slanting
portion has a length L1 smaller than a length L2 of the second
slanting portion.
According to claim 2 of the present invention, the cathode ray tube
is wherein an angle .theta.1 between the first slanting portion of
the first slanting portion and the engagement portion is larger
than an angle .theta.2 between the second slanting portion of the
second member and the fixing portion.
According to claim 3 of the present invention, the cathode ray tube
is wherein an angle .phi.1 of the first slanting portion to a tube
axis of the cathode ray tube is larger than an angle .phi.2 of the
second slanting portion to the tube axis.
According to claim 4 of the present invention, the cathode ray tube
is wherein the length L1 and the angle .phi.1 of the first slanting
portion and the length L2 and the angle .phi.2 of the second
slanting portion satisfy a relation of
L1.times.cos.phi.<L2.times.cos.phi.2.
According to claim 5 of the present invention, the cathode ray tube
according is wherein the first connection portion of the first
member is extended in a direction in which the first slanting
portion is extended.
According to claim 6 of the present invention, the cathode ray tube
comprises: a face panel having a substantially rectangular
effective portion, a side wall portion standing along a peripheral
edge portion of the effective portion, and four stud pins provided
to be projected from inner surfaces of four corner portions of the
side wall portion; a phosphor screen formed on an inner surface of
the effective portion of the face panel; a shadow mask having a
substantially rectangular mask body and a substantially rectangular
mask frame, the mask body being provided inside the face panel and
having a plurality of apertures opposed to the phosphor screen, and
the mask frame supporting a peripheral edge portion of the mask
body, being opposed to the side wall portion of the face panel, and
having a higher thermal expansion coefficient than the mask body;
four support members respectively fixed to four corner portions of
the mask frame and respectively engaged with the four stud pins of
the face panel, thereby elastically supporting the mask frame on
the face panel; an electron gun for emitting an electron beam onto
the phosphor screen through the plurality of apertures of the mask
body; and a deflector for deflecting the electron beam emitted from
the electron gun, and is wherein each of the four support members
has first and second members each formed by bending a narrow long
plate-like member having an elasticity, that the first member has
an engagement portion engaged with the stud pin, that a first
connection portion connected with the second member, and a first
slanting portion slanted and extended from the first connection
portion toward the engagement portion, in a direction in which the
first member is apart from the second member, that the second
member has a fixing portion fixed to the mask frame, a second
connection portion connected with the first connection portion of
the first member, and a second slanting portion slanted and
extended from the second connection portion toward the fixing
portion, in a direction in which the second member is apart from
the first member, that the first member has a plate-thickness d1
smaller than a plate-thickness d2 of the second member and the
first slanting portion has a length L1 smaller than a length L2 of
the second slanting portion, that an angle .theta.1 between the
first slanting portion of the first member and the engagement
portion is larger than an angle .theta.2 between the second
slanting portion of the second member and the fixing portion, and
that an angle .phi.1 of the first slanting portion to a tube axis
of the cathode ray tube is larger than an angle .phi.2 of the
second slanting portion to the tube axis.
According to claim 7 of the present invention, the cathode ray tube
according is wherein the length L1 and the angle .phi.1 of the
first slanting portion and the length L2 and the angle .phi.2 of
the second slanting portion satisfy a relation of
L1.times.cos.phi.1<L2.times.cos.phi.2.
According to claim 8 of the present invention, the cathode ray tube
is wherein the first connection portion of the first member is
extended in a direction in which the first slanting portion is
extended.
Additional objects and advantages of the invention will be set
forth in the description which follows, and in part will be obvious
from the description, or may be learned by practice of the
invention. The objects and advantages of the invention may be
realized and obtained by means of the instrumentalities and
combinations particularly pointed out hereinbefore.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
The accompanying drawings, which are incorporated in and constitute
a part of the specification, illustrate presently preferred
embodiments of the invention, and together with the general
description given above and the detailed description of the
preferred embodiments given below, serve to explain the principles
of the invention.
FIG. 1 is a cross-sectional view showing a cathode ray tube
according to an embodiment of the present invention;
FIG. 2 is a partial cross-sectional view showing a support
structure of a shadow mask in the cathode ray tube shown in FIG.
1;
FIGS. 3A to 3C are views showing a holder according to a first
embodiment of the present invention;
FIG. 4 is a graph showing a landing misregistration amount when the
length L1 of the first slanting portion of the holder is
changed;
FIG. 5 is a graph showing a landing misregistration amount when the
length L2 of the second slanting portion of the holder is
changed;
FIG. 6 is a graph showing a landing misregistration amount when the
slanting angle .phi.1 of the first slanting portion of the holder
is changed;
FIG. 7 is a graph showing a landing misregistration amount when the
slanting angle .phi.2 of the second slanting portion of the holder
is changed;
FIG. 8 is a graph showing a landing misregistration amount when the
plate-thickness d1 of the first member of the holder is
changed;
FIG. 9 is a graph showing a landing misregistration amount when the
plate-thickness d2 of the second member of the holder is
changed;
FIGS. 10A to 10C are views showing a holder according to a second
embodiment of the present invention;
FIG. 11 is a cross-sectional view showing a conventional holder;
and
FIG. 12 is a cross-sectional view showing a conventional
holder.
DETAILED DESCRIPTION OF THE INVENTION
In the following, embodiments of the present invention will be
specifically explained with reference to the drawings.
As shown in FIG. 1, the cathode ray tube 1 according to the present
invention comprises an envelope including a face panel 2 (which
will be referred to as only a panel 2 hereinafter) having a skirt
portion 2b provided and standing on the periphery of an effective
surface 2a consisting of a curved surface, and a funnel 4 connected
to the skirt portion 2b of the panel 2. A phosphor screen 6 and a
shadow mask 10 are provided in the envelope, both located inside of
the panel 2. More precisely, the screen 6 is positioned, facing the
effective surface 2a of the panel 2. The screen 2 consists of a
number of phosphor units each composed of a blue-emitting layer, a
green-emitting layer and a red-emitting layer. The shadow mask 10
opposes the phosphor screen 6.
As partially enlarged and shown in FIG. 2, the shadow mask 10
includes a mask body 8 formed by arranging a curved surface in a
substantially rectangular shape, with a number of apertures 8a
formed therein, and a substantially rectangular mask frame 9
provided at the periphery of the mask body 8. The mask frame 9 is
formed to have a substantially L-shaped cross-section bent to the
inside of the mask body 8. The mask body 8 is made of an invar
material having a relatively low thermal expansion coefficient and
a small plate-thickness, and the mask frame 9 is made of a carbon
steel plate having a higher thermal expansion coefficient than the
mask body 8.
Elastic support members 12 (which will be referred to as only
holders 12 hereinafter) are respectively fixed outside the corner
portions of the mask frame 9. The holders 12 are respectively
engaged detachably on stud pins 14 provided inside the corner
portions of the skirt portion 2b. The shadow mask 10 are suspended
on the skirt portion 2b of the panel 2 by the four holders 12.
Meanwhile, an electron gun 16 for emitting three electron beams 15
is provided in an elongated neck 4a of the funnel 4. A deflector 18
which generates a magnetic field for deflecting the three electron
beams 15 emitted from the electron gun 16 is provided outside the
funnel 4.
The three electron beams 15 emitted from the electron gun 16 are
deflected by the magnetic field generated from the deflector 18 and
are applied onto the phosphor screen 6 through the apertures 8a of
the shadow mask 10. In this manner, the phosphor screen 6 is
scanned in the horizontal and vertical directions by the electron
beams 15, and a color image is displayed through the phosphor
screen 6.
In this time, to display an image of an excellent quality without a
color drift on the phosphor screen 6 of the cathode ray tube 1,
three electron beams 15 which have passed through electron beam
apertures 8a must correctly land on three-color phosphor layers of
the phosphor screen 6, respectively. For this purpose, the
positional relationship between the panel 2 and the shadow mask 10
must be maintained correctly. In particular, the positional
relationship therebetween must be maintained with high precision in
consideration of reducing the pitch of the phosphor screen 6 to
raise the resolution.
In other words, landing positions of the electron beams 15 are
misregistered thereby causing electron beam landing
misregistration, if the positional relationship between the panel 2
and the shadow mask 10 cannot be maintained with high precision. A
thermal expansion of the mask frame 9, an impact applied from the
outside of the cathode ray tube, or the like is considered as one
of main factors which cause such misregistered landing.
The mask frame 9 is thermally expanded by a heat transferred from
the mask body 8 heated by collisions of electron beams 15. That is,
only 1/3 or less of the total electron beams emitted from the
electron gun 16 pass through the electron beam apertures 8a of the
mask body 8 and reach the phosphor screen 6. The rest of the
electron beams collide into the mask body 8. Therefore, if the
cathode ray tube 1 is operated for a long time, the mask frame 9 is
heated and the mask body 8 is accordingly heated, so that the mask
frame 9 is thermally expanded.
In case of using a shadow mask 10 having a mask body 8 made of
invar material having a relatively low thermal expansion
coefficient, the mask body 8 is not substantially deformed even
when the mask frame 9 is thermally expanded. However, in a cathode
ray tube in which the deflection angle is relatively large, the
shadow mask is moved toward the phosphor screen and misregistered
landing occurs even when conventional holders as shown in FIG. 12
are used, if a thermal expansion occurs in the mask frame 9 as a
result of operation for a long time.
Meanwhile, if an impact is applied from the outside of the cathode
ray tube 1, the engagement of the holders 12 on the stud pins 14 is
changed and the shadow mask 10 is moved undesirably, thereby
causing misregistered landing of electron beams.
From the grounds as described above, it is indispensable to reduce
misregistered landing due to the thermal expansion of the mask
frame 9 and misregistered landing due to an external impact on the
cathode ray tube 1, in order to display an image of excellent
quality in high resolution.
Therefore, the present inventors have invented a holder capable of
compensating simultaneously both the misregistered landing due to
the thermal expansion of the mask frame 9 and the misregistered
landing due to an external impact applied to the cathode ray tube
1, as a holder which elastically suspend the shadow mask 10 on the
panel 2.
FIGS. 3A to 3C show a holder 12 according to the first embodiment
of the present invention. FIG. 3A is a bottom view of the holder 12
viewed from the side of the electron gun 16. FIG. 3B is a side view
of the holder 12 viewed from the side of the skirt portion 2b of
the panel 2. FIG. 3C is a front view of the holder 12.
The holder 12 is comprised of a first member 21 having a
substantially rectangular plate-like shape, and a second member 22
having a substantially rectangular plate-like shape. The first and
second members 21 and 22 respectively have plate-thickness of d1
and d2. The first member 21 has an engagement portion where an
engagement hole 21c is formed, and the engagement hole 21c is
engaged with a stud pin 14. The second member 22 has a fixing
portion to be fixed to the mask frame 9 of the shadow mask 10. The
first and second members 21 and 22 respectively have ends 21a and
22a which are joined together by a predetermined length, and the
members 21 and 22 are bent at the end of the joining portion, in a
direction in which the member are apart from each other, thereby
making the holder 12 substantially V-shaped.
The first member 21 is further bent toward the second member 22 at
a position distant from the end of the joining portion by a length
L1. Also, this first member 21 is slightly bent toward the second
member 22 at a portion close to the other end which is apart from
the end 21a of the member 21.
The second member 22 is bent toward the first member 21 at a
position distant from the end of the joining portion by a length
L2. Thus, the first and second members 21 and 22 respectively have
slanting portions 21b and 22b having lengths L1 and L2, and are
also respectively bent at angles .theta.1 and .theta.2 at the ends
of the slanting portions, in the direction in which both members
are closer to each other.
Under a condition in which the holder 12 is properly attached
between the mask frame 9 and the skirt portion 2b (e.g., the
condition shown in FIG. 2), the slanting portion 21b of the first
member 21 is slanted at an angle .phi.1 to the direction parallel
to the tube axis of the cathode ray tube 1 (in the direction z
shown in the FIG. 2), and the slanting portion 22b of the second
member 22 is slanted at an angle .phi.2.
The misregistered landing caused by a thermal expansion of the mask
frame 9 and the misregistered landing caused by an impact from the
outside of the cathode ray tube 1, i.e., the misregistration of the
landing positions of the electron beams 15 caused by an undesirable
movement of the shadow mask 10 are thus compensated by the function
of the holders 12. The compensation amount and the compensation
direction depend on parameters such as the plate-thickness d1 and
d2 of the first and second members 21 and 22, the lengths L1 and L2
of the slanting portions 21b and 22b, the bending angles .phi.1 and
.phi.2, and the slanting angles .phi.1 and .phi.2. Note that the
compensation direction of the shadow mask 10 due to the holders 12
is a minus direction toward the electron gun 16 in case of the
cathode ray tube according to the present embodiment.
That is, the parameters of the holder 12 may have optimum values
which minimize the misregistered landing, i.e., the misregistered
landing can be minimized by setting optimum values in the
parameters. To investigate the optimum values, the parameters were
set to preset reference values at first, and the movement value of
the landing position of an electron beam was then measured as a
characteristic parameter while changing only particular
parameters.
Measurements were made of a characteristic parameter obtained in
the thermal equilibrium attained by a long operation of the tube 1,
a characteristic parameter obtained when an impact is applied to
the tube 1 in its axial direction and a characteristic parameter
obtained when an impact is applied to the tube 1 in a direction
perpendicular to the axis of the tube 1. The reference values of
the parameters of the holder 12 were set to d1=0.6 mm, d2=0.8 mm,
L1=15 mm, L2=15 mm, .phi.1=169.degree., .phi.2=163.degree.,
.phi.1=15.degree., and .phi.2=15.degree.. Further, in the graphs,
the movement amount of the landing position of the electron beam is
an average of movement amounts at respective portions of the shadow
mask 10. The measurement results in this time are shown in the
graphs of FIGS. 4 to 9.
FIG. 4 shows changes of the characteristic parameter (PL) when only
the length L1 of the slanting portion 21b of the first member 21 is
changed. FIG. 5 shows changes of the characteristic parameter (PL)
when only the length L2 of the slanting portion 22b of the second
member 22 is changed. FIG. 6 shows changes of the characteristic
parameter (P.phi.) when only the slanting angle .phi.1 of the
slanting portion 21b is changed. FIG. 7 shows changes of the
characteristic parameter (P.phi.) when only the slanting angle
.phi.2 of the slanting portion 22b is changed. FIG. 8 shows changes
of the characteristic parameter (Pd) when only the plate-thickness
d1 of the first member 21 is changed. FIG. 9 shows changes of the
characteristic parameter (Pd) when only the plate-thickness d2 of
the second member 22 is changed. In each graph, the smaller the
movement amount of the landing position is, i.e., the smaller the
characteristic parameter is, the smaller the misregistered landing
can be.
As can be seen from FIGS. 4, 5, 8, and 9, the characteristic
parameter during operation for a long time tends to be repulsive to
the characteristic parameters when external impacts (e.g., an
impact in the tube axis direction and an impact in the short edge
direction), where the lengths L1 and L2 of the slanting portions
21b and 22b of the holder 12 are changed, and when the
plate-thickness d1 and d2 of the members 21 and 22 are changed.
Therefore, to reduce the movement of the landing position of the
electron beam caused by a thermal expansion of the mask frame
during operation for a long time while restricting also the
movement of the landing position of the electron beam caused by
external impacts, it is desirable that the lengths L1 and L2 of the
slanting portions and the plate-thickness d1 and d2 are set to
values close to the cross points in the figures. From the values
close to the cross points in the graphs, it is known that relations
of L1<L2 and d1<d2 exist. Therefore, misregistered landing
can be reduced by setting respective parameters so as to satisfy
the relations of L1<L2 and d1<d2.
Meanwhile, as can be seen from FIGS. 6 and 7, the misregistered
landing caused by operation for a long time and that caused by an
external impact can be reduced by enlarging both the slanting
angles .phi.1 and .phi.2 of the slanting portions 21b and 22b to
the tube axis of the cathode ray tube 1. However, if the slanting
angles .phi.1 and .phi.2 are too large, it hinders the
detachability of the holder 12. In addition, there are limitations
to the size of the holder 12, so that .phi.1+.phi.2 is restricted
in accordance with the distance between the stud pin 14 and the
mask frame 9.
From comparison between the FIGS. 6 and 7, it can be seen that the
ratio of the change of the landing position of the electron beam,
i.e., the inclination of the characteristic line is greater when
.phi.1 is changed than when .phi.2 is changed. Therefore,
misregistered landing can be reduced more when .phi.1 is changed
prior to .phi.1. In consideration of these respects, the slanting
angles of the slanting portions 21b and 22b should preferably be
set so as to satisfy the relation of .phi.1>.phi.2.
In addition, since the fixing portion where the second member 22 is
fixed to the mask frame 9 is parallel to the tube axis of the
cathode ray tube 1, the engagement portion with the stud pin 14 of
the first member 21 needs to be inclined to the tube axis in order
to obtain a spring pressure enough to engage the shadow mask 10.
Therefore, the bending angle should desirably set so as to satisfy
.theta.1>.theta.2.
Thus, by setting respective parameters of the holder 12 so as to
satisfy the relations of L1<L2, d1<d2, .phi.1>.phi.2, and
.phi.1>.phi.2, the misregistered landing caused by a thermal
expansion of the mask frame 9 and the misregistered landing caused
by an external impact can simultaneously be compensated so that an
image of high quality without a color drift can be displayed
stably.
For example, where the sizes of the first and second members 21 and
22 of the holder 12 were set to L1=15.6 mm, .phi.1=19.52.degree.,
.theta.1=169.0.degree., d1=0.6 mm, L2=16.11 mm,
.phi.2=17.35.degree., .theta.2=162.6.degree., and d2=0.8 mm, the
movement amount of the landing position of the electron beam was
improved as follows in comparison with a conventional holder
(having d1=0.5 mm, d2=0.8 mm, and L1>L2 for reference). That is,
the distance the beam-landing position moved in the long operation
of the tube 1 was reduced from +44 .mu.m to +24 .mu.m and improved
by about 45% on average for the entire surface of the mask 10; the
distance the beam-landing position moved due to the externally
applied impact was decreased from 17 .mu.m to 14 .mu.m and improved
by about 18% on average for the peripheral part of the mask 10, and
decreased from 50 .mu.m to 37 .mu.m and improved by 26% at maximum.
In this example, the lengths L1 and L2 of the slanting portions 21b
and 22b of the holder 12 and the slanting angles .phi.1 and .phi.2
thereof with respect to the tube axis satisfied a relation of
L1.times.cos.phi.1<L2.times.cos.phi.2. It has been found that
the movement amount of the landing position of the electron beam
can be reduced more and misregistered landing can be reduced where
the relation exists.
The present invention is not limited to the embodiment described
above, but can be variously modified within the scope of the
invention. For example, FIGS. 10A to 10C show a holder 30 according
to a second embodiment of the present invention.
The holder 30 has rectangular plate-like first and second members
21' and 22. The joining portion where the first member 21' is
joined together with the second member 22 is arranged to extend in
the direction in which the slanting portion 31 extends. Thus, the
detachment of the holder 30 can be more facilitated if the joining
portion of the first member is shaped in form an extension of the
slanting portion 31.
Additional advantages and modifications will readily occur to those
skilled in the art. Therefore, the invention in its broader aspects
is not limited to the specific details and representative
embodiments shown and described herein. Accordingly, various
modifications may be made without departing from the spirit or
scope of the general inventive concept as defined by the appended
claims and their equivalents.
* * * * *